Siloxane compounds and silicones have found many uses in modern industry. For example, siloxane compounds are widely used in the production of cross-linked silicone polymers. These polymers typically are produced by either a hydrosilylation reaction or a condensation reaction. In the hydrosilylation reaction, siloxane compounds bearing vinyl groups undergo addition to link individual molecules of the compounds through the formation of new Si—C bonds. The hydrosilylation reaction typically is catalyzed by platinum, which contributes to the cost of these polymers since the platinum cannot be recovered from the cured elastomer. In the condensation reaction, the siloxane compounds react in a condensation reaction to form new Si—O—Si linkages between individual molecules. This condensation reaction produces volatile organic compounds (VOCs) as a by-product.
An alternative method for producing cross-linked silicone polymers utilizes starting materials containing cyclic siloxane moieties. In the polymerization reaction, these starting materials are combined with a suitable base. The base attacks and breaks some of the siloxane linkages present in the cyclic siloxane moieties. When these siloxane linkages are broken, the two ends of the broken siloxane linkage are converted to silanolate ions. These silanolate ions then react with other silanolate ions and/or siloxane linkages (e.g., siloxane linkages in the cyclic siloxane moieties present on other molecules of the starting materials) to produce new siloxane linkages and cross-links between the different molecules of the starting materials. The product of this reaction is a cross-linked silicone polymer. Typically, a strong base is employed to ensure that the polymerization reaction proceeds quickly and to the desired degree. To achieve optimal hardness, these systems typically are cured at temperatures of 70-100° C. However, at such cure temperatures, the reaction mixture takes a relatively long time to gel. While this extended gel time may not be detrimental for certain uses, the extended gel time has been found to be problematic when certain particulate materials are added to the mixture, such as LED phosphors. In such instances, the phosphors, which are relatively dense, can settle before the reaction mixture gels. In order to shorten the gel time, higher temperatures can be used, but these higher temperatures can deleteriously affect the hardness of the cured siloxane network (silicone polymer).
A need therefore remains for compositions and methods that are capable of producing high quality cross-linked siloxane networks (e.g., cross-linked silicone polymers) under the desired conditions. The compositions and methods described herein seek to address this unmet need.